Most everyday listening environments consist of a multitude of sounds, many of which are fluctuating in level over time. The way in which the brain sifts apart this acoustic complex into its constituent sound sources is referred to as auditory perceptual organization. The root interest of this project is in understanding the role that temporal processing play in perceptual organization, and how impaired auditory systems can compromise this ability. The project pursues two lines of investigation. The first seeks to identify changes in temporal processing that may occur relatively early in the aging process, and to differentiate these from effects of cochlear hearing loss. The second line of investigation examines perceptual organization in listeners with cochlear implants. The project incorporates both psychophysical land electrophysiological paradigms. A total of 75 listeners will participate across a spectrum of experiments. Data will be analyzed using descriptive statistics, tests of correlation, and analyses of variance. The project will lead to a clearer understanding of how complex sounds are perceptually organized in both acoustic and electric hearing, and how changes in the auditory system due to age and hearing loss may affect this ability.